The stage production of “Ghost” features Caissie Levy and Richard Fleeshman (far left and below) in a famed pottery scene that Demi Moore and Patrick Swayze (left) made famous in the 1990 film. Photo: Hartman Group PR

(Hartman Group PR)

There are two kinds of people: those who want to leave a classic movie alone — Harper Lee and the 1962 film of her “To Kill a Mockingbird” spring to mind — and those who want to turn it into a musical.

One look at Broadway tells you Lee’s in the minority, especially in a season that brings us “Once,” “Newsies,” “Leap of Faith” and “Ghost: The Musical.” The last just materialized at the Lunt-Fontanne, where it opens April 23 following spirited reviews from London’s West End.

As anyone who’s seen the 1990 weepie can tell you — a show of handkerchiefs, please! — the film pretty much had everything: special effects, star-crossed lovers (a strapping Patrick Swayze and a pre-Ashton Kutcher Demi Moore as Sam and Molly), a great Righteous Brothers song (“Unchained Melody”) . . . and a really hot pottery scene.

It also made half a billion dollars and won an Oscar for Whoopi Goldberg as a sassy psychic pressed into playing a go-between for the couple after Sam — a shy guy who mutters “ditto” whenever Molly says she loves him — is murdered.

Even so, “Ghost” writer Bruce Joel Rubin was in Harper Lee’s camp: He wanted to leave a good flick alone.

“My biggest fear,” he says, “was that they’d sing some strange little ‘Ditto’ song that would make my skin crawl!”

Enter Colin Ingram, a producer with no such qualms about putting big-screen triumphs on the stage.

“You have to choose a movie that’s inherently theatrical,” says the man who helped turn “Billy Elliot” into “Billy Elliot: The Musical.”

“ ‘Ghost’ has all the big scenes a musical should have: comedy, revenge, tragedy,” he says. “It’s very Shakespearean, actually.” (Then again, the formula isn’t foolproof. Ingram’s “Gone With the Wind: The Musical” blew away after 79 London performances.)

As a college student in Edinburgh, Ingram saw “Ghost” with his girlfriend, but never considered it a chick flick. He loved the special effects, the drama and action. About six years ago, after the producer Tony Adams suggested doing the show, it fell to Ingram to persuade Rubin to climb aboard the “Ghost” express.

“Colin and [producer] David Garfinkel came to my place in upstate New York, and we talked so long they missed their train back to the city,” recalls Rubin, whose film was inspired by his time in a Tibetan monastery, which left him thinking that life might well continue after death.

“By the morning, I realized there was so much more to the emotional life of the characters that, put into song, would deepen the story.” Rubin became so excited that he wrote 20 lyrics for the show before director Matthew Warchus basically told him to stop.

“Matthew said, ‘We have two of the best songwriters working on the show — can’t we let them take it from here?’ ” Since those writers were Dave Stewart of pop-rock’s Eurythmics (“Sweet Dreams”) and his producing partner Glen Ballard, Rubin didn’t argue.

“We had the script, and we worked alongside Bruce for quite a while,” Stewart says. “I would be writing songs on the spot with Glen, collaborating. This process went on for three or four years until we eventually had all the songs locked in.”

But how do you ditch a song like “Unchained Melody,” the heart of the film? You don’t — though how and when that song comes up may surprise you. (Spoiler alert: Sam has a guitar, and he’s not afraid to strum it.) Nor was there a ghost of a chance the show would lose its clay play.

“Everyone who talks about ‘Ghost’ talks about the pottery scene,” Rubin sighs, but though his wife’s a potter, that movie scene wasn’t his idea — it was his director, Jerry Zucker’s. Rubin originally wanted Molly to sculpt in big chunks of wood to let viewers know she was strong enough to handle a world without Sam. (Jerry Zucker, a grateful world thanks you.)

Of course, you can’t stage “Ghost” without magic: When your leading man is dead for most of the show, illusions are clearly in order. So the “Ghost” team signed Paul Kieve, who taught Daniel Radcliffe a trick or three for “Harry Potter and the Prisoner of Azkaban.”

“There were a number of challenges,” concedes Kieve, who started doing magic tricks 34 years ago, when he was 10. “Bodies splitting from their spirits — or the other way around — walking through doors, jumping into bodies, and a stylistic thing we do in the subway, with everything going in slow motion and then out of it.”

Making those illusions work required an across-the-board effort from the actors, writers, video, sound and lighting crews. Kieve says it’s also a matter of knowing what not to take from the film. A ghost tap-dancing and levitating in the air? Not gonna happen. “In the movie, it’s a throwaway thing,” he says, “but onstage it would be a major moment.

“This isn’t a magic show,” he adds. “It’s a story that happens to integrate illusion. We’re not putting the film onstage. We’re putting the story.”

If the word from London, where the show’s still playing, is any indication, “Ghost: The Musical” also keeps the movie’s spirit intact by staying true to its New York setting — the London props people have flown in 300 empty pizza boxes from Brooklyn to use on the set.

“The word many people have used about our show is ‘surprising,’” Ingram says. “Surprisingly good, surprisingly not cheesy, surprisingly different from the film but retaining a lot of the film’s assets.